DeForest Columbian 7D634 hum

[Robert]

Hi everyone,

Just found this amazing resource!

As the title says, this baby is humming.

I picked it up about 30-odd years ago at a flea market in Montreal for 50 bucks. I replaced a few of the tubes (Radio Hovsep in Montreal still had tons), and it worked fairly well. Ever since shortwave started taking a nosedive, I stopped using it, and it was just a lovely piece of furniture.

I’m now in Victoria (where electronic parts are impossible to find locally), and I’ve decided to resurrect it.

There was some serious 60Hz hum when I fired it up, so I yanked out the electrolytic cans and replaced them with modern caps. 60Hz hum gone, mostly.

Now there’s a (probably) 120Hz hum that sits at noise level, then ramps up when a station is pulled in on AM (there’s only 1 in Victoria)

I’m not sure where to go from here. I’ve also swapped out the 3 high voltage .1uf caps, but it didn’t do anything.

Any and all suggestions would be appreciated.

For context, I’m a 68 year old retired microwave radio hardware designer (2-18 GHz LNAs, mixers, PAs, filters, etc), but know virtually nothing about vacuum tubes.

Thanks

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[Dan Walker]

Hi Robert;
I have worked on several of these rogers and Deforest Crosley radios.
I have been doing it for about 20 years, and am am self taught, with the help of the Antique radio forum and the Canadian vintage radio society.
That does not mean much except after working on several of these radios I find that ALL the capacitors need to be changed
I don’t have the schematic for that model in front of me , but there might be a one or two bias cells in the radio.
Rogers and Marconi used them a lot.
The mica caps don’t need to be changed but the rest of them need to be replaced.
You can send me a Private Message and I can send you an email .

Do you have the schematic of the radio? These are very nice radios and they play good when restored.
Dan Walker in Calgary

[Tom Stevens]

Try adding an EMI filter. I get a lot of electrical “Noise” in my house wiring and had to build a power bar with a 10Amp EMI filter installed in it. I had similar problems until I started using the EMI filter.

[Tom Stevens]

Also, if you get an EMI filter, DO NOT connect the ground wire. None of my radios or power supplies have 3 pin plugs so the ground is irrelevant. I was getting a noticeable hum when testing TRFs with ABC power supply and also my vintage stereo stuff and the EMI filter cleared it right up. See attached photo

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[westcoastjohn]

Hello Robert and welcome to the club. AM radios are so hungry for fresh input these days, they will pull noise out of the air. Regulations have gone slack.
Are you tuning in CFAX, Victoria’s only AM station, Vancouver CBC 690 or CKNW 730? Unplug phone chargers and other digital devices anywhere near your radio. If you have a transistor radio, see if it plays quiet. A portable can be used as a noise sniffer.

North of the Malahat I don’t even try to pick up CFAX. Where you are you can get Bellingham and Seattle KIXI 880, “Music as cool now as it was then”. Their format has changed to more talk but they still play music part of the time.

There is a good source for tubes, sockets and other parts right in Esquimalt, John’s PacificTV.com. Get schematics for free from John’s website and send him some business. That goes for anyone reading these pages, use it or we lose it.

• This reply was modified 3 weeks ago by westcoastjohn.

[westcoastjohn]

Here’s a link to the schematic and a couple of clips that we can study. Nothing like a bit of homework, oh yeah.
https://pacifictv.ca/schematics/rogers12-61data.pdfHopefully the noise is controllable but if it is indeed an internal problem, we can find ways to eliminate it on the schematic. Maybe. 🙂

• This reply was modified 3 weeks ago by westcoastjohn.

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[westcoastjohn]

https://pacifictv.ca/schematics/rogers12-61data.pdf

Let us know if this info matches your set. They are ID’ed more by given name than by number, but there are duplicate chassis in the Majestic and Rogers cabinets,
3 different cabinets have identical schematics.

[Author]

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